Enhancing the circular polarization degree of NIR-II circularly polarized light of cellulose nanocrystal films

Circularly polarized light in the second near-infrared window (NIR-II CPL) features a unique set of advantages such as deep penetration depth and reduced light absorption, which holds promising potentials for biomedical applications. To date, high-performance NIR-II CPL materials remain challenging to construct. Here, we report that the application of ultrasonication to cellulose nanocrystal (CNC) suspensions red-shifts the film photonic bandgap to the NIR region; in concurrent, focal conic phase forms whose intercalation within self-assembled chiral nematic CNC films can be eliminated by keeping the film thickness below a critical value. We present that multilayer lamination of thin CNC films absence of focal conic phase affords a general approach to produce right-handed NIR-II CPL with the degree of circular polarization of 0.556 at 1430 nm. Finally, we demonstrate that the right-handed CPL at 1430 nm of the laminated CNC film offers an extra optical diagnostic tool for the discrimination of human cancer tissues.